As many as 140 pilot whales died after becoming stranded on Mason Bay on the west coast of the island.
Doc was alerted to the stranded whales at 10.30pm on Saturday by a tramper camping in the area.
Around half the whales had died by the time they were discovered, and the remaining whales had to be euthanised, Doc Rakiura Operations Manager Ren Leppens said.
"Sadly, the likelihood of being able to successfully re-float the remaining whales was extremely low. The remote location, lack of nearby personnel and the whales' deteriorating condition meant the most humane thing to do was to euthanise.''
There were a number of a reasons whale strandings occurred, including sickness, navigational error, geographical features, a rapidly falling tide, being chased by a predator, or extreme weather.
Low tide in the area had been around .5m and high tide around 2.8m, meaning the tidal range, the difference between low and high tide, had been "reasonably big'', a MetService spokesman said.
Several strandings happened throughout the country over the weekend.
On Sunday 10 pygmy killer whales stranded at 90 Mile Beach, a sperm whale beached in Doubtful Bay on Karikari Peninsula in Northland, and a dead female pygmy sperm whale washed up at Ohiwa.
University of Otago zoology lecturer Prof Liz Slooten said strandings were unfortunately not unusual.
Last year nearly 650 whales stranded over two days at Farewell Spit, at the north end of Golden Bay.
The whales lived in extended family groups, and if even one or two members of the group got into trouble - for instance if they were sick, elderly, having difficulty giving birth, or could not use echolocation properly - the others felt compelled to stay to help, she said.
"The rest of the group won't leave.''
They hunted for food, fended off predators and navigated the oceans as a group. However, they could survive in smaller pods, and if 50 had stranded it would have been possible for the others to survive, Prof Slooten said.
The best way to discover the cause of the stranding would be to conduct an autopsy on the whales that had stranded first, although that would be difficult to determine now.
The most common place to strand was Farewell Spit. The particular geography of the spit, which had shallow beach shelves, confused the whales.
Loud noises, for instance navy sonar or air guns used in oil and gas exploration, could cause the whales to lose their bearings.
Project Jonah general manager Darren Glover said
New Zealand was a "global hot-spot for whale strandings. We have more strandings statistically than any other country on record.''
There had been a number of mass whale strandings, particularly in the Mason Bay area, partly due to its ``gently-shelving sandy beaches'' he said.
"What we do find with almost every stranding, there's more than one reason ... sometimes we can put it down to a combination of four, five, even six different factors that may have led to the stranding.''
Doc notified local Ngai Tahu iwi and were working on the next steps to take.
